"Modifications had to be made," Pitt acknowledged. "But it wouldn't take any great engineering feat to remove the conning tower and other projections until the top deck fitted flush against the mother ship's keel. The average fleet-type sub of World War II had a displacement of fifteen hundred tons, a length of over three hundred feet, a hull height of ten feet, and a beam of twenty-seven feet—roughly twice the size of a suburban house. Once the torpedo rooms, the eighty-man-crew quarters and the unnecessary paraphernalia were cleared out there would be more than ample space to store the heroin."

Pitt saw that Zacynthus was regarding him in a very peculiar manner: there was a deep look of contemplation on his face. Then his features showed the first traces of genuine understanding.

"Tell me, Major," he asked. "What speed could the Queen Artemisia make with a sub fastened to her hull?"

Pitt thought a moment. "I'd say about twelve knots. Unencumbered, however, the ship's normal cruising speed would be closer to fifteen or sixteen."

Zacynthus turned to Zeno. "It's quite possible the major's on the right track."

"I know what you are thinking, my Inspector." Zeno's teeth parted beneath the great moustache. "We have often concerned our thoughts with the puzzling variance of the cruising speeds among Minerva ships."

Zacynthus' eyes came back to Pitt. "The heroin drop, when and how is it made?"

"At night during high tide. Too risky during the day. The sub could be spotted from the air—"

"That checks," Zacynthus interrupted. "Von Till's freighters are always scheduled to reach port after sunset."

"As to the drop"—Pitt hadn't even taken notice of the interruption—"the sub is released immediately after entering port. Without a conning tower or periscope it must be guided from the surface by a small craft. Here, the only real chance of failure comes in, being rammed in the dark by an unsuspecting vessel."

"No doubt they'd have a pilot on board who was familiar with every inch of the harbor," Zacynthus said thoughtfully.

"A first-rate harbor pilot is an absolute necessity for an operation like von Till's," Pitt agreed. "Dodging underwater obstacles over a shallow bottom in the dark is no exercise for an amateur yachtsman."

"The next problem on the agenda," Zacynthus said slowly, "is to determine the location where the sub can unload and distribute the heroin without fear of detection."

"How about a deserted warehouse?" Giordino volunteered. His eyes were closed and he looked like he was dozing, but Pitt knew from long experience that he hadn't missed a word.

Pitt laughed. "The evil villain who slinks around deserted warehouses went out with Sherlock Holmes. Waterfront property is at a premium. An idle building would only arouse instant suspicion. Besides, as Zac here can tell you, a warehouse would be the first place an investigator would look."